Extraction solvent control for reducing stable emulsions

Abstract

Disclosed herein are methods for recovering diphosphonite-containing compounds from mixtures comprising organic mononitriles and organic dinitriles, using multistage countercurrent liquid-liquid extraction. Recovery is enhanced with one or more method steps. In a first step, a portion of the heavy phase from the settling section of the first stage is recycled to the settling section of the first stage. In a second step, a portion of the light phase from the settling section of the first stage is recycled to the mixing section of the first stage. In a third step, the first stage takes place in a mixer-settler, a Lewis base is introduced into the settling section of the first stage, and a complex of Lewis acid and Lewis base is formed in this settling section. In a fourth step, a polyamine is added to the first stage.

What is claimed is: 
     
       1. A process for recovering diphosphonite-containing compounds from a feed mixture comprising diphosphonite-containing compounds, organic mononitriles, organic dinitriles and a Lewis acid in a multistage countercurrent liquid-liquid extractor with extraction solvent comprising aliphatic hydrocarbon, cycloaliphatic hydrocarbon or a mixture of aliphatic and cycloaliphatic hydrocarbon, said process comprising:
 a) flowing the feed mixture to the first stage of the multistage countercurrent liquid-liquid extractor; and 
 b) contacting the feed mixture with extraction solvent in the multistage countercurrent liquid-liquid extractor,
 wherein the multistage countercurrent liquid-liquid extractor comprises at least 2 stages, wherein each stage of the multistage countercurrent liquid-liquid extractor comprises a mixing section and a settling section, wherein the mixing section provides a mixed phase comprising a light phase and a heavy phase, wherein a light phase separates from a heavy phase in the settling section, wherein a mixed phase, which comprises both a heavy phase and a light phase, is present in the settling section between the light phase and the heavy phase, wherein the light phase comprises extraction solvent and extracted diphosphonite-containing compounds, wherein the heavy phase comprises organic mononitriles and organic dinitriles, wherein at least a portion of the light phase is withdrawn from the settling section of the first stage and treated to recover diphosphonite-containing compounds extracted into the light phase, wherein at least a portion of the heavy phase from the first stage is passed to the second stage of the multistage countercurrent liquid-liquid extractor, wherein fresh extraction solvent is fed to the final stage, wherein light phase from the second stage is fed to the first stage, and wherein the process further comprises at least one of the following additional steps: 
 (i) withdrawing a portion of the heavy phase from the settling section of the first stage of the multistage countercurrent liquid-liquid extractor and recycling the withdrawn heavy phase to the settling section of the first stage of the multistage countercurrent liquid-liquid extractor; or 
 (ii) withdrawing a portion of the light phase from the settling section of the first stage of the multistage countercurrent liquid-liquid extractor and recycling the withdrawn light phase to the mixing section of the first stage of the multistage countercurrent liquid-liquid extractor. 
 
 
     
     
       2. The process of  claim 1 , wherein a portion of the heavy phase is withdrawn from the settling section of the first stage of the multistage countercurrent liquid-liquid extractor and recycled to the settling section of the first stage of the multistage countercurrent liquid-liquid extractor, wherein a raffinate recycle ratio (RRR) is between 0.1 and 0.9, wherein RRR is defined by the ratio of X to Y, wherein X is the mass per unit time of the portion of the heavy phase recycled to the settling section of the first stage of the multistage countercurrent liquid-liquid extractor, and wherein Y is the mass per unit time of all of the heavy phase withdrawn from the settling section of the first stage of the multistage countercurrent liquid-liquid extractor. 
     
     
       3. The process of  claim 2 , wherein the RRR is between 0.2 and 0.8. 
     
     
       4. The process of  claim 1 , wherein at least one stage of the extraction is carried out above 40° C. 
     
     
       5. The process of  claim 1 , wherein a portion of the light phase is withdrawn from the settling section of the first stage of the multistage countercurrent liquid-liquid extractor and recycled to the mixing section of the first stage of the multistage countercurrent liquid-liquid extractor, wherein an extraction solvent recycle ratio (ESRR) is between 0.1 and 0.9, wherein ESRR is defined by the ratio of X′ to Y′, wherein X′ is the mass per unit time of the portion of the light phase recycled to the mixing section of the first stage of the multistage countercurrent liquid-liquid extractor, and wherein Y′ is the mass per unit time of all extraction solvent charged to the mixing section of the first stage of the multistage countercurrent liquid-liquid extractor. 
     
     
       6. The process of  claim 5 , wherein the ESRR is between 0.2 and 0.8. 
     
     
       7. The process of  claim 1 , wherein the extraction solvent is cyclohexane. 
     
     
       8. The process of  claim 1 , wherein the feed mixture is an effluent stream from a hydrocyanation process. 
     
     
       9. The process of  claim 8 , wherein the hydrocyanation process includes a 3-pentenenitrile hydrocyanation process. 
     
     
       10. The process of  claim 9 , wherein the hydrocyanation process includes a 1,3-butadiene hydrocyanation process. 
     
     
       11. The process of  claim 1 , wherein the Lewis acid is ZnCl 2 .